Lithographic printing plate imaging process



31, 1965 n. A. NEWMAN 3,203,344

LITHOGRAPHIC PRINTING PLATE IMAGING PROCESS Filed Feb. 13, 1961 mmvrozz. Douylaa A, A cwmam ATTORNEYS United States Patent 3,203,344 LITHOGRAPHIC PRINTING PLATE IMAGING 'PRGCESS Douglas A. Newman, Glen Cove, N.Y., assignor to Columbia Ribbon and Carbon Manufacturing Co., Inc.,

Glen Cove, N.Y., a corporation of New York Filed Feb. 13, 1961, Ser. No. 88,745 4 Claims. (Ql. 101-1492) This invention relates to a novel method of imaging printing plates and to the novel sheets for carrying out the same.

Lithographic printing plates are conventionally imaged unde pressure as by typing or writing on the hydrophilic surface thereof with an imaging composition which is oleophilic in nature. The thus imaged plate is then inked with a conventional lithographic ink composition which is oleaginous and adheres to the oleophilic imaged areas while being repelled by the unimaged hydrophilic areas of the plate. Such a system allows for the preparation of numerous duplicate copies.

It has been found that there are many instances in which it is inconvenient or impossible to manually apply the oleophilic images to the surface of the printing plate, such as for instance when the printing plate is too wide to fit a typewriter or is a continuous roll such as is used in the field of pattern-making and the like.

It has also been found that the manual imaging of plates, as by writing or typing thereon, results very often in the application of erroneous images to the plate surface and these errors or mistakes must be corrected by either erasing them or by discarding the plate and starting anew. Although the plate surface is sufiiciently strong in most instances to provide for the making of erasures, care must be taken that the hydrophilic surface coating is not disrupted or removed or else the plate will fail.

Another disadvantage inherent in the process of imag ing lithographic plates manually stems from the fact that the plate surface is hydrophilic and oleophobic and thus tends to repel the adhesion of oleophil-ic images thereto. Unless care is taken in the writing or typing of these images onto the plate surface, the images may tend to flake-off or be removed during the process of preparing duplicate copies in the printing process.

It is therefore an object of the present invention to image lithographic plates without the necessity of applying any imaging pressure to the surface of the plate.

It is another object of this invention to image lithographic printing plates directly with an imaged donor I sheet thereby avoiding any chance of applying erroneous images to the surface thereof.

It is still another object of this invention to heat fuse oleophilic images to a lithographic plate surface thereby preventing the images from flaking-off or being removed during the printing process.

These and other objects and advantages will be apparent from the following description and claims as well as from the accompanying drawing.

In the drawing:

FIGURE 1 is a perspective view of an imaged original or donor sheet shown together with a transfer sheet having a transfer composition 21 with which it has been imaged.

FIG. 2 is a diagrammatic cross section, to an enlarged view, of the imaged original or donor sheet 10 superposed with a lithographic plate 30, separated for purposes of illustration, and under the effects of infrared radiation.

FIG. 3 illustrates the sheets of FIG. 2, after irradia- 3,203,344 Patented Aug. 31, 1965 tion, demonstrating the images 30a transferred from sheet 10 to the surface of the lithographic plate.

The objects of the present invention are accomplished, as demonstrated by the accompanying drawing, through the use of an original or donor sheet 10 bearing surface images 11 which consist of a composition which is oleophilic in nature, absorbs infrared radiation and converts it to heat, and has a melting point in the range of from about F. to about 250 F.

These images 11 may be in either direct-reading positive form or in reverse-reading mirror-reverse form depending upon the nature of the printing process in which the final lithographic plate is to be employed.

The original or donor sheet foundation 10 may be either paper or a clear plastic film such as cellophane or Mylar but in any event it must be relatively translucent so as to transmit infrared radiation to the images 11 on the underside thereof. The translucency of the donor sheet has the added advantage that it allows the images on the underside of the donor sheet to be visible or proofread through the top or unimaged side as images 12, illustrated by FIG. 1 of the drawing. This is of particular importance when the images 11 are in mirror-reverse form as shown in FIG. 1.

The images 11 are placed upon the donor sheet by superposing sheet 10 in surface contact with the transfer layer 21 of transfer sheet 29 and applying imaging pressure against either sheet 10 or sheet 20 depending upon the form of the images desired. When the imaging pressure is applied by means of a typewriter, it is preferred to remove the typing ribbon so that the type bars make direct contact with either sheet 10 or 2th and effect the transfer of sharper images than possible when a ribbon is used.

The composition of the transfer layer 21 forms a critical part of the present invention in that such composition becomes transferred to the plate or copy sheet surface in the form of images 30a which comprise the inkreceptive imaged areas thereon. The transfer layer must contain a transfer composition which is oleophilic and thus has an afiinity for the conventional oleaginous lithographic printing inks. The composition must also have the property of absorbing infrared radiation and converting it to heat. Likewise it must have a melting point within the range of about 100 F. to about 250 P. which is the temperature range generated by conventional infrared radiation devices.

Additionally it has been found preferable that the transfer composition be so constituted as to have no sharp melting temperature so that the melting of the composition in the form of images 11 takes place over a temperature range of several degrees. In this manner, the images first soften and adhere sharply to the plate surface and the over-all melting of the images occurs slowly and gently. If a composition having a sharp melting temperature is employed, then the images 11 liquefy suddenly and abruptly and tend to spread on the plate surface causing the formation of wide blurred lithographic images. Excellent results have been obtained in this regard when the transfer composition contains amixture of different binder materials, either waxes or thermoplastic resins or preferably mixtures thereof, having different melting temperatures, together with an infrared radiation-absorbing pigment such as nigrosine and/or carbon black.

The following examples demonstrate transfer compositions which provide excellent results according to the present invention. However, it must be pointed out that these compositions are set forth by way of illustration and should not be construed as limitative.

Example 1 Ingredients: Parts by weight Carnauba wax 45 Beeswax Indopol H-300 (polymerized butene isomers) 15 Nigrosine 20 Mineral oil 20 Example 2 Ingredients: Parts by weight Raw montan wax 40 Parafiin 5 Vistanex (polyisobutylene) Nigrosine Carbon black 10 Rapeseed oil Example 3 Ingredients: Parts by weight Microcrystalline wax 15 Carnauba wax 20 Tornesit (chlorinated rubber) 2O Nigrosine Mineral oil 15 Lanolin 5 The translucent donor sheet imaged with any of the above compositions is next superposed with any suitable conventional lithographic printing plate so that the images 11 are in surface contact with the hydrophilic surface of the plate. The sheets are then subjected to a light source rich in infrared radiation which is directed onto the donor sheet, as demonstrated by FIG. 2, for a period of time suflicient to melt the images 11 and allow them to adhere to the plate surface. Upon removal of the sheets from the radiation source and separation thereof, portions of images 11 have been picked off by the plate surface in the form of oleophilic images 30:: as shown by FIG. 3, leaving remnant portions 11a on the donor sheet available for the imaging of additional lithographic plates in the same manner, if so desired. Or, if desired, the used donor sheet may be stored as a permanent record copy.

The imaged lithographic plate may be used in conventional lithographic printing processes to produce 300 to 400 sharp duplicate copies.

The nature of the lithographic plate 30 used in the present process is not critical and conventional flexible plates having hydrophilic surfaces based upon carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, gelatin, zein, etc. may be advantageously imaged as taught herein.

It has been found that the use of infrared radiation forms a critical part of the present invention in that it allows for selective heating of the images on the donor sheet without materially heating the donor sheet and the lithographic printing plate. The heated images transfer sharply and cleanly to the plate surface, and this is critical in the printing art where the quality of the several hundred duplicate copies which are produced from the plate depends ultimately upon the quality of the lithographic images on the plate. It has been found that when heat is used to cause transfer, rather than infrared radiation, then the donor sheet and lithographic plate are also heated overall, and the images 11 tend to lose their sharpness by melting and spreading on the warm or hot donor sheet, and by being even further spread by the warm or hot surface of the lithographic plate, thereby resulting in dull or fuzzy images on the final plate and very inferior lithographic copies.

No particular criticality exists with respect to the source of infrared radiation employed and'infrared ray lamps, carbon arcs and photoflash lamps provide excellent results. It is generally preferred to employ any convenient flat bed apparatus or belt machine such as the Thermo- Fax machine. The duration of exposure of the sheet is continued for only that period of time sufficient to reduce the images 111 to a melted condition, generally anywhere from instantaneous to about five or ten seconds, depending upon the proximity and strength of the radiation source.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. The method of placing oleophilic images on the surface of a lithographic printing plate through the use of infrared radiation, which comprises:

(a) superposing an infrared radiation-translucent donor sheet and a transfer sheet having a pressure-sensitive transfer layer comprising heat-meltable, oleophilic, infrared radiation-absorbing composition having a melting point within the range of from about F. to about 250 F,

(b) applying pressure to said superposed sheets to transfer said composition to the surface of said donor sheet in image form,

(c) superposing a flexible lithographic printing plate with its working surface in contact with said image on said donor sheet,

(d) directing a sufficient quantity of radiation rich in infrared against the donor sheet to selectively heat the image to a temperature within the range of from about 100 F. to about 250 F. to cause it to melt and adhere to the working surface of the plate without materially heating the infrared radiation-translucent donor sheet, and

(e) separating said sheets to form the plate having the oleophilic image thereon in an area corresponding to the image area of the donor sheet.

2. The method of claim 1 in which the pressure-sensitive transfer layer on the transfer sheet comprises a mixture of different wax binder materials having different melting temperatures so that the transfer layer has no sharp melting temperature and the melting thereof takes place over a temperature range of several degrees.

3. The method of claim 1 in which the pressure-sensitive transfer layer comprises a mixture of wax and thermoplastic resin binder materials having different melting temperatures so that the transfer layer has no sharp melting temperature and the melting thereof takes place over a temperature range of several degrees.

4. The method of claim 1 in which the composition of the transfer layer has no sharp melting temperature so that the melting thereof takes place over a temperature of several degrees.

References Cited by the Examiner UNITED STATES PATENTS 2,243,078 5/41 Bjorksten et a1. 10l-149.4 2,616,961 11/52 Groak 101-1492 X 2,721,821 10/55 Hoover 101-426 X 2,808,777 10/57 Roshkind 101-149.2 2,954,311 9/60 Vander Weel 101149.5

FOREIGN PATENTS 1,165,125 5/58 France. 1,228,426 3/60 France.

OTHER REFERENCES Senefelder: Complete Course of Lithography, published 1819, R. Ackerman, London. Only pages 121 and 258 made of record.

DAVID KLEIN, Primary Examiner.

ROBERT A. LEIGHEY, Examiner. 

1. THE METHOD OF PLACING OLEOPHILIC IMAGES ON THE SURFACE OF A LITHOGRAPHIC PRINTING PLATE THROUGH THE USE OF INFRARED RADIATION, WHICH COMPRISES: (A) SUPERPOSING AN INFRARED RADIATION-TRANSLUCENT DONOR SHEET AND A TRANSFER SHEET HAVING A PRESSURE-SENSITIVE TRANSFER LAYER COMPRISING HEAT-MELTABLE, OLEOPHILIC, INFRARED RADIATION-ABSORBING COMPOSITION HAVING A MELTING POINT WITHIN THE RANGE OF FROM ABOUT 100* F. TO ABOUT 250*F., (B) APPLYING PRESSURE TO SAID SUPERPOSED SHEETS TO TRANSFER SAID COMPOSITION TO THE SURFACE OF SAID DONOR SHEET IN IMAGE FORM, (C) SUPERPOSING A FLEXIBLE LITHOGRAPHIC PRINTING PLATE WITH ITS WORKING SURFACE IN CONTACT WITH SAID IMAGE ON SAID DONOR SHEET, (D) DIRECTING A SUFFICIENT QUANTITY OF RADIATION RICH IN INFRARED AGAINST THE DONOR SHEET TO SELECTIVELY HEAT THE IMAGE TO A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 100*F. TO ABOUT 250*F. TO CAUSE IT TO MELT AND ADHERE TO THE WORKING SURFACE OF THE PLATE WITHOUT MATERIALLY HEATING THE INFRARED RADIATION-TRANSLUCENT DONOR SHEET AND (E) SEPARATING SAID SHEETS TO FORM THE PLATE HAVING THE OLEOPHILIC IMAGE THEREON IN AN AREA CORRESPONDING TO THE IMAGE AREA OF THE DONOR SHEET. 